FIG. 20 is a diagram of a conventional communications equipment employing a conventional antenna duplexer. In FIG. 20, the conventional antenna duplexer includes antenna terminal 201, switch 202 electrically connected to this antenna terminal 201 for switching to multiple systems, and first and second antenna duplexers 203 and 204 switched by this switch 202. First antenna duplexer 203 is an antenna duplexer for a first system, and includes transmit filter 203a and receive filter 203b. Transmit filter 203a is electrically connected to transmit amplifier 205 and transmit circuit 209A. Receive filter 203b is electrically connected to low-noise amplifier 206 and receive circuit 210A. Second antenna duplexer 204 is an antenna duplexer for a second system, and includes transmit filter 204a and receive filter 204b. Transmit filter 204a is electrically connected to transmit amplifier 207 and transmit circuit 209B. Receive filter 204b is electrically connected to low-noise amplifier 208 and receive circuit 210B.
This structure realizes an antenna duplexer that allows the selective use of multiple systems. A prior art related to the present invention is, for example, disclosed in Patent Literature 1.
However, this conventional antenna duplexer is difficult to be downsized. This is because a transmit filter and a receive filter are needed for every system according to the number of selectable systems in the conventional antenna duplexer.    Patent Literature 1: Japanese Patent Unexamined Publication No. 2004-228666